The present invention relates to a process and a plant for the treatment of vulcanized rubber of all kinds, such as tyres, conveyor belts, boots, shoes and other objects containing assembled rubber and polymer materials for the purpose of recycling the components by the relevant industries.
The bulk of these materials is represented above all by the increase in road transport development which gives rise to worrysome quantities of downgraded tyres difficult to remove and possibly to recycle.
It should not be forgotten that more than 3 billion tyres, merely from private vehicles, are running along the roads in the various countries and, of course, have to be periodically replaced. In terms of weight, this represents at least 18 million tonnes of bulky waste which has to be disposed of, something which represents a serious ecological problem difficult to solve, and above all since people are becoming increasingly aware of environmental problems and regulations.
A vast quantity of tyres is destroyed by incineration and in cement kilns with recovery of thermal energy. This approach is being increasingly questioned because of the atmospheric pollution and of the destruction of materials which are beneficial to recover.
Another process consists of successive grinding so as to end up with small particles that can be used as fillers in bitumens and asphalts. Such grinding has been facilitated by cryogenic techniques. However, multiple shredders, which are indispensable for shearing the metal reinforcements, in order to produce reusable powder, are heavy machines which devour energy and are consequently very expensive.
Another destruction process, with recovery of certain components, is based on pyrolysis. The recycling consists in recovering the pyrolysis oil, the carbon and the metals. These processes are high-performance processes but they require the investment of large sums of money and high treatment costs, they are often the source of significant atmospheric pollution.
Thus efforts have been intensified to develop methods for stripping this bulky waste in a manner which is effective, economical and environmentally non-polluting. Considerable research has been focused on the problem, which obviously does not concern only worn tyres but all manufactured products made of rubber and also the waste accompanying the manufacture of these products, these often being reinforced with metal reinforcements or reinforcements made of synthetic materials. The ultimate problem does not reside only in the economical destruction of the rubber element or of the tyres, but it is also desirable to be able to recover and reuse them, or some of the components, for the purpose of avoiding unnecessary wastage of beneficial materials.
With the aim of illustrating the prior art in this field, it is appropriate to mention the following publications:                GB 2,026,144 (1979) discloses a plant for the treatment of rubber waste and of synthetic materials coming from worn tyres. Thermal decomposition of the product, which is coarsely reduced, is carried out in a fluidized bed of sand at 800° C. in the presence of oxygen. The gases produced by the decomposition are used and, at the end of the process, the reinforcing metals are recovered by means of magnets.        U.S. Pat. No. 4,426,459 (prior. JP 1980) discloses a process for the decomposition of vulcanized rubber by a treatment around 100° C. with an organic solvent in the presence of an alkaline hydroxide such as potassium hydroxide.        DE 3,313,470 (1983) relates to a method and to an apparatus for treatment at a temperature above 200° C. for 10 to 35 minutes in a liquid phase composed of spent mineral oils and of organic solvents. A viscous product is obtained which can be used as an additive in bitumens or insulation layers.        WO 97/1561 (prior. U.S. 1995 and 1996) describes a process for the devulcanization of rubber coming from downgraded tyres by desulphurization at around 300° C. by means of an alkali metal in a medium that does not contain oxygen, before or during a treatment by an organic solvent after having separated the constituents of the tyres, such as the steel and other reinforcements.        
Many of these processes have disadvantages, namely from the standpoint of the investments, of the efficiency, of the complexity, of the environment or of the market.